Wafer prober for enabling efficient examination

ABSTRACT

A control unit of a wafer prober for implementing wafer examination, using a probe card including a multiple number of probes, executes a multiple number of measuring operations by bringing the probes of the probe card into contact with bonding pads formed on a wafer and by measuring the electric characteristics between predetermined pads of the bonding pads, each of the measuring operations being implemented after varying the relative position between the probe card and the wafer, in directions parallel to the face of the wafer. The control unit, upon execution of each of the measuring operations, implements the measuring operation after adjusting the relative position between the probe card and the wafer so that the contact position of each probe of the probes against each pad of the bonding pads is separated from all the positions at which the probes have already touched that pad of the bonding pads for a predetermined number of different times.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wafer prober that automaticallybrings probes into contact with pads of multiple chips formed on a waferand tests chip characteristics.

2. Description of the Related Art

Generally, in the semiconductor manufacturing process, devices andconductive patterns that constitute a plurality of chips 51 are formedon the surface of, typically disk-shaped, wafer 50 as shown in FIG. 1.Wafer 50 with devices and conductive patterns formed thereon is thendiced along the predetermined scribe lines so as to produce individual,typically square-shaped, chips 51 to be the products. In thissemiconductor manufacturing process, it has been known as a practice tomeasure the characteristics of chips 51 formed on wafer 50 before chips51 are separated, by using a wafer prober so as to examine whether anydefective chips 51 are present.

As a wafer prober, a configuration has been known which uses a probecard having a multiple number of probes formed in a predetermined planarpattern so that they will come into contact with a multiple number ofbonding pads, typically made of aluminum and formed on chips 51. Thiswafer prober performs test of each chip 51 by precisely positioning itsprobe card relative to wafer 50 so that the probes come into contactwith the bonding pads of each chip 51 at predetermined positions and bymeasuring electric characteristics between the bonding pads.

Thereafter, the wafer prober is moved relative to wafer 50 in order toexamine different chips 51 on wafer 50 because the probe card isgenerally smaller than wafer 50. Thus, multiple shots for measurementare performed for single wafer 50. In this process, if the probes touchthe same location on the same bonding pad several times due to multipleshots for measurement, there is a risk that the bonding pad might bebadly scratched or might be peeled off in some cases, causing theproblem that chip 51 cannot be correctly connected to the mountingsubstrate or the like.

To avoid this, in conventional wafer probers, a test is performed byvarying the placement of the probe card relative to wafer 50 from oneshot to another so that no probes will touch the same bonding pad. Inother words, the placement of the probe card relative to wafer 50 at thetime of each shot for measurement is performed in accordance with aplacement pattern (a wafer shot pattern or a wafer shot map) in whichthe probe card is positioned relative to wafer 50 at the time ofmultiple shots for measurement, so that one area on the wafer covered bythe probe card at the time of one shot does not overlap with anotherarea covered thereby at the time of another shot. The square frame linesin FIG. 1 show one example of this wafer shot pattern. That is, eachframe indicates the placement position of the probe card at the time ofeach measurement is taken.

In the example shown in FIG. 1, when the wafer probe is positioned overthe area near the periphery of wafer 50, only a relatively low number ofchips 51 can be examined by one shot for measurement. Moreover, in somecases depending on the sizes of wafer 50 and probe card 52, it could benecessary to perform one shot for measurement for a still lower numberof chips 51. In this way, there are cases where examination throughputbecomes inefficient due to low flexibility of the wafer shot pattern.

On the other hand, Japanese Patent Application Laid-open 60-117638discloses a wafer manufacturing process in which a multiple number offunctional tests are implemented under different conditions such asnormal temperature, high temperature, low temperature and the like. Inthis case, in order to avoid an adverse effect due to contacts of theprobe against the same location of any bonding pad, a multiple number ofprobe cards are used, which are differentiated from each other in apattern of probes so that each pattern of probes comes into contact withbonding pads at different positions from those of another pattern.

SUMMARY OF THE INVENTION

The object of the present invention is to improve the efficiency ofwafer examination by a probe card.

In order to achieve this object, a wafer prober according to the presentinvention comprises a probe card. The probe card has a multiple numberof probes arranged in a predetermined pattern so as to be able to bringthe probes into simultaneous contact with bonding pads of multiplesemiconductor chips formed on a wafer. The wafer prober furthercomprises two means for changing the relative position between the probecard and the wafer, and a control unit. One of the means is to changethe relative position between a position at which the probes touch thebonding pads and a position at which the probes are separated from thebonding pads. The other of the means is to change the relative positionin directions parallel to the face of the wafer. The control unitcontrols the operations of the two means for changing the relativeposition between the probe card and the wafer so as to separate theprobes of the probe card from the bonding pads, and to subsequentlyadjust the positional relation between the probe card and the wafer withrespect to directions parallel to the face of said wafer, and tosubsequently bring said probes of the probe card into contact with thepredetermined pads of the bonding pads, and which implements a measuringoperation for measuring the electric characteristics via the designatedpads of the bonding pads. The control unit successively implements themeasuring operations multiple times in accordance with a setup pattern,wherein the measuring operations are implemented under differentconditions in which the relative position between the probe card and thewafer is varied in directions parallel to the face of the wafer. At thistime, the control unit implements the measuring operations afteradjusting the relative position between the probe card and the waferupon execution of each of the measuring operations such that the contactposition of each probe of the probes against each pad of the bondingpads is separated from all the positions at which the probes havealready touched that pad of the bonding pads for a predetermined numberof different times.

According to the present invention, even in a case where the wafer shotpattern is so set up that the same boding pads are touched by probesseveral times during a multiple number of measuring operations and whenthe number of times the probes come into contact with the same bondingpad will exceed a predetermined number of times, the contact positionsof probes against the bonding pads are automatically adjusted so thatprobes will not touch the same positions on the bonding pads for morethan the predetermined number of different times. Thereby, if the probestouch the identical bonding pad at a greater number of different timesthan the predetermined number, it is possible to Inhibit damage to thebonding pad that results from probes making contact with the pad.Accordingly, it is possible to improve the flexibility of the wafer shotpattern, and hence crate an efficient examination by setting up anappropriate wafer shot pattern.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description withreference to the accompanying drawings which illustrate examples of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a wafer which is examined by means of a waferprober, and also shows a pattern of placement of a probe card, whichdetermines the movement of the prove card, of a conventional waferprober for different measurements;

FIG. 2 is a block diagram showing a schematic configuration of a waferprober of one embodiment of the present invention;

FIG. 3 is a plan view of a wafer which is examined by means of a waferprober shown in FIG. 2, and also shows a pattern of placement of a probecard for different measurements;

FIG. 4A is a side view showing a probe being brought into contact with abonding pad formed on a wafer by means of a wafer prober shown in FIG.2;

FIG. 4B is a plan view showing contact positions of probes;

FIG. 5 is a block diagram showing a schematic configuration of a waferprober of an alternative example of FIG. 2; and

FIG. 6 is a block diagram showing a schematic configuration of a waferprober of another alternative example of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 2, the wafer prober of the present embodiment includeswafer stage 1 on which wafer 20 under test is mounted and probe card 10supported at a predetermined position over wafer stage 1. This waferprober also includes control unit 5 made up of a computer etc., forcontrolling the operation of each part based on a predetermined program.

Wafer stage 1 is precisely adjustable as to position by amplifier 2. Theposition of wafer stage 1 is detected by position encoder 3. Further,alignment mark 25 is previously formed at a predetermined position onwafer 20. The position of alignment mark 25 is detected by means ofcamera 4 and image recognizer 7. These detected signals are input tocontroller 6. Controller 6 can actuate amplifier 2 and adjust theposition of wafer 20, supported on wafer stage 1, to a predeterminedposition based on these input signals.

As schematically shown in FIG. 3, a multiple number of chips 21 areformed on wafer 20. Each chip of chips 21 is formed with a predeterminedpattern of bonding pads 22 (see FIGS. 4A and 4B) that can beelectrically connected to the mounting substrate etc.

Probe card 5 has a planar size which is smaller than wafer 20 but cancover some chips of chips 21 formed on wafer 20. Formed on the surfaceof probe card 10 facing wafer stage 1 are probes 11 (see FIGS. 4A and4B) having a planar pattern corresponding to a predetermined pattern ofbonding pads 22 on each chip of chips 21. That is, when probe card 10and wafer stage 1 are put closer to each other while wafer 20 supportedon wafer stage 1 is adjusted and kept to the predetermined positionrelative to probe card 10 in the directions parallel to the face ofwafer 20, each probe of probes 11 comes into contact with each pad ofbonding pads 22 at a predetermined position which is the approximatecenter of the individual pad of bonding pads 22, as indicated byreference numeral 23 of FIG. 4B, for example.

The relative position between probe card 10 and wafer 20 with respect tothe directions parallel to the face of wafer 20 can be preciselyadjusted by aforementioned wafer stage 1. It is also possible to adjustprobe card 10 and wafer 20 between the position at which probes 11 ofprobe card 10 and bonding pads 22 on wafer 20 are put in contact and theposition at which they are positioned away from each other, by movementof wafer stage 1.

Alternatively, probe card 10 can be moved closer to or away from thesurface of wafer stage 1 on which wafer 20 is supported, by means of anappropriate actuator.

Further, though not illustrated, the wafer prober includes a tester unitfor measuring the electric characteristics via some probes of probes 11.Though not detailed, control unit 5 has the function of actuating thistester unit to measure the electric characteristics via previouslydetermined probes of probes 11 of probe card 5, hence via predeterminedpads of bonding pads 22 in each chip of chips 21. Further, control unit5 can have the function of determining whether each chip of chips 21 isfree from defects. Moreover, control unit 5 can have the function ofadjusting the relative position between wafer 20 supported on waferstage 1 and probe card 10 in accordance with a previously determinedpattern of placement for different measurements, i.e., a wafer shotpattern, by actuation of amplifier 2 upon start of individualmeasurement, subsequently by measuring, and by performing theseoperations repeatedly so as to measure all the predetermined chips 21 onwafer 20. Further, control unit 5 can have the function of determiningpass/failure during the above operations.

Next, one example of wafer examination by the wafer prober of thisembodiment will be described.

As stated above, the wafer prober performs a series of multiple shotsfor measurement while sequentially moving wafer stage 1 in accordancewith a previously determined wafer shot pattern. FIG. 3 shows the areaswith reference to wafer 20, which are covered by probe card 10 whenindividual shots for measurement take place, with square frame lines.

The shots for measurement are sequentially performed from the areaenclosed by the upper left frame line in FIG. 3 to the adjacent areas,for example. At this time, each of the six framed areas located on theupper side in FIG. 3, which are covered by probe card 10 over wafer 20when each measurement takes place, is allocated so as not to overlap theothers.

On the other hand, the two framed areas located on the lower side inFIG. 3, which are covered by probe card 10 over wafer 20 when eachmeasurement takes place, overlap the framed areas located above thosetwo framed areas, at the sections designated by reference numeral 26.Therefore, probes 11 will touch the pads of bonding pads 22 twice, whichare the pads belonging to the chips of chips 21 that are located withinthe sections designated by reference numeral 26.

In this case, when the wafer prober of the present embodiment implementsmeasurement at the positions indicated by two frame lines located at thebottom in FIG. 3, the wafer prober will appropriately adjust theposition of probe card 10 relative to wafer 20 so that each of probes 11will touch the corresponding pads of bonding pads 22 at a positionmarginally away from the position at which the previous touch was made.More specifically, for example, upon the measurement at the positionsindicated by the six upper frame lines in FIG. 3, each of probes 11 isbrought into contact with the central portion of bonding pads 22, asindicated by reference numeral 23 of FIG. 4B. In contrast, upon themeasurement at the positions indicated by the two lower frame lines inFIG. 3, probes 11 are brought into contact with a position marginallyshifted above, in FIG. 4B, from the center of bonding pads 22,designated by reference numeral 24 in FIG. 4B.

In this way, when probes 11 are brought into contact with the same padof bonding pads 22, it is possible to inhibit enlargement of the damageon that pad of bonding pads 22, that results from probes 11 touchingthat pad of bonding pads 22, and it is also possible to prevent a largepart of that pad of bonding pads 22 from peeling off. Accordingly, inaccordance with the present embodiment, it is possible to choose a wafershot pattern in a manner that allows the areas, which are covered byprove card 10 over wafer 20 when multiple shots for measurement takeplace, to overlap one another without any damage of bonding pads 22 ofchips 21, hence it is possible to improve flexibility of the wafer shotpattern. As a result, the operator of the wafer prober is able to set upan appropriate wafer shot pattern in accordance with the sizes of wafer20 and probe card 10 and the like, such that examination efficiency isimproved. In contrast to the conventional example shown in FIG. 1 wherenine shots for measurement are needed, eight shots for measurement areenough to perform examination of similar wafer 20 in the example shownin FIG. 3. In this way, efficiency of examination throughput isimproved.

Although the above testing process was described taking an example whereidentical bonding pads 22 in the areas designated by numeral 26 aretouched twice by probes 11, it is also possible to allow the operator toset up a pattern of placement of probe card 10 in which some identicalpads of bonding pads 22 are touched by probes 11 at three or moredifferent times. In this case, it is possible to shift the contactpositions of some probes of probes 11 to the same pads of bonding pads22 at three or more different times, so that all the contact positionsare different from each other

Next, description will be made of a more specific configuration ofcontrol unit 5 that performs shifting control of the contact positionsof probes 11 to bonding pads 22 among multiple shots for measurementduring which some pads of bonding pads 22 are brought into contact withprobes 11 at a multiple number of different times as in the above case.

In the configuration of the present embodiment shown in FIG. 2, controlunit 5 has shot information storage 8 and contact position informationstorage 9. Controller 6 stores information of the positions of the chipsof chips 21 on wafer 20, which undergo the characteristic measurement,that is, which are touched with probes 11 of probe card 10 for thecharacteristic measurement, into shot information storage 8 when a shotfor characteristic measurement is made. At the same time, controller 6also stores information of the position, at which each probe of probes11 touches each pad of bonding pads 22, in contact position informationstorage 9, while linking this information with the information in shotinformation storage 8. For this purpose, the information of the contactposition may be stored, for example, in the form of a combination of anoffset direction and an offset distance from a standard position, thestandard position being set at a central position of bonding pads 22.

After taking shots for measurement, controller 6 moves wafer stage 1 tothe position for taking the next shot for measurement in accordance withthe wafer shot pattern. At this time, information from shot informationstorage 8 is read out and it is judged whether the chips of chips 21 tobe measured at the next measurement position include the chips of chips21 that have already been measured during the previous shot formeasurement. From this, if any chips of chips 21 that have already beenmeasured during the previous shot for measurement are included in thechips of chips 21 to be measured next, the information of the positionsof individual bonding pads 22 where probes 11 touched during theprevious shot for measurement is read out and an offset direction andoffset distance that can avoid contact at the same positions, areselected

For example, the way of this selection can be previously determined asfollows: the offset is set at 0 if chips that have been touched byprobes 11 up to this point are not included in the chips to be measured;the offset direction is set to be upward if only the chips of chips 21that have been touched once by probes 11 are included in the chips ofchips 21 to be measured next; the offset direction is set to be downwardif the chips of chips 21 that have been touched twice by probes 11 areincluded; the offset direction is set to be rightward if the chips ofchips 21 that have been touched at three different times by probes 11are included. Alternatively, it is also possible to select an offsetdirection and offset distance in a random fashion, from amongalternatives, in which probes 11 will not touch the same position ofbonding pads 22, and which are included in multiple predeterminedalternatives in which the offset direction and distance have been set.

Controller 6 then computes the shift position of wafer stage 1 takinginto account the selected offset direction and offset distance and moveswafer stage 1. That is, the position at which the next shot formeasurement is implemented by probe card 10 is selected at the positionthat deviates in the selected offset direction by the selected offsetdistance from the standard position that is determined in accordancewith the wafer shot map.

In accordance with this configuration, it is possible for the operatorof the wafer prober to implement examination so that bonding pads 22 arenot damaged due to repeated contacts of probes 11, by performing arelatively easy setup of a wafer shot map, that is, by making a roughsetup for determining the standard positions of individual shots formeasurement (e.g., setting up the areas of chips 21 which should betouched by probes 11 at the time of individual shots for measurement).In other words, the operator can freely set up a shot map, and thencontroller 6 automatically avoids multiple contacts of probes 11 on thesame position on each pad of bonding pads 22. Accordingly, it is nolonger necessary for the operator to set up a wafer shot map by takinginto account whether bonding pads 22 of chips 21 will be touched at amultiple number of different times by probes 11 or to set up how toavoid bonding pads 22 being touched at the same positions by probes 11when the same chips are touched at a multiple number of different times.

Next, another configurational example of control unit 5 is shown in FIG.5.

In the example shown in FIG. 5, control unit 5 has contact positioncalculator 30 for calculating the positions of probe needle scars formedon bonding pads 22 by contact with probes 11 based on the image signalinput from camera 4 via image recognizer 7. Upon execution of each shotfor measurement, contact position calculator 30 judges whether any probeneedle scar has been formed on each pad of bonding pads 22, which probes11 of probe card 20 will touch at the time of the next shot, andcalculates the position at which the probe needle scar is formed on eachpad of bonding pads 22.

If any probe needle scars are found on the pads of bonding pads 22 whichprobes 11 of probe card 10 will touch at the time of the next shot formeasurement based on the input from contact position calculator 30,controller 6 moves wafer stage 1 to a position that deviates from thestandard position for each pad of bonding pads 22 so that probes 11 willcome into contact with positions that deviates from the probe needlescars and controller 6 implements measurement. The position shiftingoperation at this time can be made similarly to the case of theconfiguration shown in FIG. 2, based on, for example, the predeterminedalternatives in which the offset direction and offset distance is set.

Next, still another configurational example of control unit 5 is shownin FIG. 6.

In the configuration shown in FIG. 6, control unit 5 has chipinformation storage 40 for storing information of the number of timeseach chip of chips 21 on wafer 20 is touched by probes 11. In thisconfiguration, upon execution of each shot for measurement, controller 6reads out the number of times that chips 21 have been touched by probes11 for all the chips of chips 21 that will be touched by probes 11 ofprobe card 10 during the next shot. Controller 6 then selects theposition on bonding pads 22, at which probes 11 will be brought intocontact for the next shot, based on the greatest number of times thatthe chips of chips 12, which will be touched by probes 11 during thenext measurement, have been touched by probes 11 of probe card 10. Forexample, it is possible to set up beforehand the positions of contactthat vary depending on the number of contacts that have been made beforemeasurement, such that contact will made at the center of boding pads 22when no contact has been made during the previous shot, and contact willbe made at a position that is shifted upwards by a predetermined offsetdistance from the center when one contact has been made, and so on.

After the shot for measurement, for all the chips of chips 21 that havebeen touched by probes 11 during that measurement, information about thenumber of contacts stored in chip information storage 40 is rewritten bythe addition of one to the greatest number of times that any of thechips, which were touched by probes 11 during that measurement, has beentouched during the previous measurement. With this configuration, it ispossible to avoid having probes 11 touch the same position of the samepads of bonding pads 22 at a multiple number of different times.

The embodiment and alternative examples described heretofore are mereexamples of the present invention, and various modifications can beadded within the scope of the invention. For example, although the aboveexample was described by referring a configuration in which probes 11are prevented from touching the same positions of the same pad ofbonding pads 22, it is possible to provide a configuration, for example,in which probes are permitted to touch the same position twice, whereasmaking contact three or more times will be prevented. Alternatively, itis possible to provide a configuration in which, if a probe needle scar,based on the image of the probe needle scar formed on bonding pads 22,that is greater than the predetermined size is found on a pad of bondingpads 22, contact of probes 11 against that pad of bonding pads 22 atthat position will be avoided.

1. A wafer prober comprising: a probe card having a multiple number ofprobes arranged in a predetermined pattern so as to be able to bringsaid probes into simultaneous contact with bonding pads of multiplesemiconductor chips formed on a wafer; a means for changing a relativeposition between said probe card and said wafer, between a position atwhich said probes touch said bonding pads and a position at which saidprobes are separated from said bonding pads; a means for changing therelative position between said probe card and said wafer, in directionsparallel to a face of said wafer; and a control unit which controlsoperations of said two means for changing the relative position betweensaid probe card and said wafer so as to separate said probes of saidprobe card from said bonding pads, and to subsequently adjust positionalrelation between said probe card and said wafer with respect todirections parallel to the face of said wafer, and to subsequently bringsaid probes of said probe card into contact with predetermined pads ofsaid bonding pads, and which subsequently implements a measuringoperation for measuring electric characteristics between designated padsof said bonding pads, wherein said control unit successively implementsthe measuring operations multiple times in accordance with a setuppattern, the measuring operations being implemented under differentconditions in which the relative position between said probe card andsaid wafer is varied in directions parallel to a face of said wafer; andsaid control unit implements said measuring operations after adjustingthe relative position between said probe card and said wafer uponexecution of each of said measuring operations such that a contactposition of each probe of said probes against each pad of said bondingpads is separated from all the positions at which said probes havealready touched that pad of said bonding pads for a predetermined numberof different times.
 2. The wafer prober according to claim 1, whereinsaid control unit adjusts the relative position between said probe cardand said wafer so that the same pad of said bonding pads will not betouched at the same position for two or more different times by saidprobes.
 3. The wafer prober according to claim 1, wherein said controlunit stores into a storage information about pads of said bonding padswhich said probes touch at each of said measuring operations, and uponthe start of each of said measuring operations, adjusts the relativeposition between said probe card and said wafer based on the informationread out from said storage so that each probe of said probes comes intocontact with each pad of said bonding pads at a position separated fromall the positions at which said probes have already touched that pad ofsaid bonding pads for a predetermined number of different times duringprevious operation of said measuring operations.
 4. A wafer probercomprising: a probe card having a multiple number of probes arranged ina predetermined pattern so as to be able to bring said probes intosimultaneous contact with bonding pads of multiple semiconductor chipsformed on a wafer; a means for changing a relative position between saidprobe card and said wafer, between a position at which said probes touchsaid bonding pads and a position at which said probes are separated fromsaid bonding pads; a means for changing the relative position betweensaid probe card and said wafer, in directions parallel to a face of saidwafer; a control unit which controls operations of said two means forchanging the relative position between said probe card and said wafer soas to separate said probes of said probe card from said bonding pads,and to subsequently adjust positional relation between said probe cardand said wafer with respect to directions parallel to the face of saidwafer, and to subsequently bring said probes of said probe card intocontact with predetermined pads of said bonding pads, and whichsubsequently implements a measuring operation for measuring electriccharacteristics between designated pads of said bonding pads; and ameans for determining a position of a probe needle scar formed on saidbonding pads through contact of said probes against said bonding pads,using a captured image of said wafer, wherein said control unitsuccessively implements the measuring operations multiple times inaccordance with a setup pattern, the measuring operations beingimplemented under different conditions in which relative positionbetween said probe card and said wafer is varied in directions parallelto a face of said wafer; and said control unit, upon the start of eachof said measuring operations, actuates said means for determining theposition of the probe needle scar so as to acquire the information ofthe position of the probe needle scar for all the pads of said bondingpads which said probes will touch at that operation of said measuringoperations, and adjusts the relative position between said probe cardand said wafer based on that information, so that each probe of saidprobes comes into contact with each of pads of said bonding pads thatwill be touched during that operation of said measuring operation, at aposition separated from all the positions at which the probe needle scaris formed.
 5. A wafer testing method of implementing a multiple numberof measuring operations by bringing a multiple number of probes formedon a probe card into simultaneous contact with bonding pads of multiplesemiconductor chips formed on a wafer and by measuring electriccharacteristics between predetermined pads of said bonding pads, themeasuring operations being implemented after automatically changing arelative position between said probe card and said wafer in accordancewith a setup pattern, wherein each of said measuring operations isimplemented after adjusting the relative position between said probecard and said wafer upon execution of each of said measuring operationsso that a contact position of each probe of said probes against each padof said bonding pads is separated from all the positions at which saidprobes have already touched that pad of said bonding pads for apredetermined number of different times.
 6. A program for causing acomputer to execute the wafer testing method according to claim 5.